In motor vehicles, it is desirable to minimize the heat transfer between the ambient engine compartment air and the air being admitted to the engine whether the engine intake air be cold or is heated such as by the exhaust manifold. In the former case, it is desirable to reduce the heat transfer from the engine compartment air to the engine intake air to improve engine performance. On the other hand, in the latter case the objective is to reduce heat loss from the heated engine intake air to the engine compartment air to allow a desired calibrated engine air intake temperature to be reached sooner. Heretofore the practice has been to use various insulation materials for both heat transfer reduction and noise attenuation as well as various mechanical muffler devices with respect to the latter. While such arrangements have generally proven satisfactory, they have been found in light of the discovery of the present invention to be relatively costly and complex particularly with respect to noise attenuation.